Methods and devices for delivering pulsed RF energy during catheter ablation

ABSTRACT

Method and devices for delivering pulsed RF ablation energy to enable the creation of lesions in tissue are disclosed. The delivery of RF energy is controlled such that the generator power setting remains sufficiently high to form adequate lesions while mitigating against overheating of tissue. An ablation catheter tip having high-thermal-sensitivity comprises a thermally-insulative ablation tip insert supporting at least one temperature sensor and encapsulated, or essentially encapsulated, by a conductive shell. A system for delivering pulsed RF energy to a catheter during catheter ablation comprises an RF generator and a pulse control box operatively connected to the generator and configured to control delivery of pulsatile RF energy to an ablation catheter comprising at least one temperature sensor mounted in its tip. Also disclose is a method of controlling the temperature of an ablation catheter tip while creating a desired lesion using pulsatile delivery of RF energy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional patent applicationNo. 62/141,066, filed 31 Mar. 2015, and 62/198,114, filed 28 Jul. 2015,both of which are hereby incorporated by reference as though fully setforth herein.

BACKGROUND OF THE DISCLOSURE

a. Field

The present disclosure relates to low thermal mass ablation cathetertips (also known as high-thermal-sensitivity catheter tips) and tosystems for controlling the delivery of RF energy to such cathetersduring ablation procedures.

b. Background Art

RF generators used during catheter ablation procedures are often set ina “temperature control” mode, and the power is initially set to a valuethat is sufficiently high (for example, 35 Watts) to create lesions intissue and the tip temperature is set to, for example, 40° C. As soon asthe tip reaches 40° C., the power is titrated down to a lower powersetting such as, for example, 15 Watts to maintain the 40° C. targettemperature. This can, however, create problems in that such lower powersettings (e.g., 15 Watts) may be too low to create lesions that are deepenough to be effective for treating abnormal heart rhythms.

The foregoing discussion is intended only to illustrate the presentfield and should not be taken as a disavowal of claim scope.

BRIEF SUMMARY OF THE DISCLOSURE

It is desirable to be able to control the delivery of RF energy to acatheter to enable the creation of lesions in tissue by keeping thegenerator power setting sufficiently high to form adequate lesions whilemitigating against overheating of tissue.

In an embodiment, an ablation catheter tip havinghigh-thermal-sensitivity comprises a thermally-insulative ablation tipinsert comprising a first portion and a second portion, wherein theinsert is adapted to support at least one temperature sensor; aconductive shell comprising a shell distal end portion and a shellproximal end portion, wherein the conductive shell is adapted to fitaround the first portion of the insert in thermally-conductive contactwith the at least one temperature sensor; and a shank adapted to coverthe second portion of the insert, whereby the conductive shell and theshank are conductively connected and together effectively encase theablation tip insert. The at least one temperature sensor may comprise aplurality of temperature sensors, and the first portion of the tipinsert may comprise a plurality of longitudinally-extending sensorchannels, wherein each temperature sensor in the plurality oftemperature sensors is mounted in a corresponding one of the pluralityof longitudinally-extending sensor channels.

In another embodiment, an ablation tip for an ablation cathetercomprises (a) a thermally and electrically conductive housing comprisinga conductive shell that comprises an inner surface; (b) athermally-insulative tip insert, wherein the conductive shell surroundsat least a portion of the tip insert; (c) at least one thermal sensormounted on the tip insert in thermally-transmissive contact with theinner surface of the conductive shell, wherein the at least one thermalsensor is configured to receive and report temperature feedback receivedvia the conductive shell; and (d) a wired or wireless communicationpathway communicatively connected to the at least one thermal sensor andconfigured to facilitate reporting the temperature feedback to anablation control system.

In yet another embodiment, a system for delivering pulsed RF energyduring catheter ablation comprises a generator configured to generate RFenergy; a pulse control box operatively connected to the generator andconfigured to control delivery of the RF energy and adapted to deliverthe RF energy in a pulsatile manner; and an ablation catheter comprisingat least one temperature sensor mounted in a tip of the ablationcatheter, and wherein the ablation catheter is operatively connected tothe pulse control box and adapted to communicate tip temperature to thepulse control box.

In another embodiment, a system for controlling the delivery of energyto an ablation catheter during an ablation procedure comprises: anablation generator capable of being operated in a power-control mode; aninput device for entering a desired ablation power level; an inputdevice for entering a desired temperature setpoint; and a pulse controlbox adapted to receive temperature feedback from the ablation catheterduring a catheter ablation procedure, wherein the pulse control box isconfigured to pulse delivery of ablation energy to the ablation catheterat the desired ablation power level during the catheter ablationprocedure while keeping the received temperature feedback at or close tothe desired temperature setpoint.

In an embodiment, a method of controlling a temperature of a tip of anablation catheter while creating a desired lesion in tissue comprises(A) placing a generator in a power-control mode; (B) setting thegenerator to deliver RF power to the tip (i) at a power level sufficientto create a lesion and (ii) for an initial time; (C) setting a pulsecontrol to a first setpoint; (D) monitoring the temperature of the tip;(E) commencing pulsed control of the RF power delivered to the tip oncethe monitored tip temperature approaches the first setpoint; and (F)continuing to deliver pulsed RF power to the tip until the desiredlesion is complete.

In still another embodiment, a method for controlling the delivery ofenergy to an ablation catheter during an ablation procedure comprises(i) setting an ablation generator to a power-control mode; (ii)inputting a desired ablation power level; (iii) inputting a desiredtemperature setpoint; (iv) initiating an ablation cycle; (v) monitoringcatheter tip temperature; and (vi) initiating pulsed control of theenergy delivered to the ablation catheter when the monitored cathetertip temperature reaches or closely approaches the desired temperaturesetpoint.

The foregoing and other aspects, features, details, utilities, andadvantages of the present disclosure will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a highly-schematic representation of one embodiment of asystem for delivering pulsed RF energy during catheter ablation, showingpossible communication pathways between primary components in thisembodiment.

FIG. 2 is similar to FIG. 1, but depicts the components arranged in aslightly different configuration in an alternative embodiment of asystem for delivering pulsed RF energy during catheter ablation.

FIG. 3 is similar to FIGS. 1 and 2, but depicts a system with adedicated central processing unit interfacing with the components alsodepicted in FIGS. 1 and 2.

FIG. 4 schematically depicts a catheter in use in a patient andconnected to a generator comprising a pulsed RF control system accordingto the present disclosure.

FIG. 5 depicts one possible control flowchart, including variousoptional steps, for delivering pulsed RF energy to an ablation catheter.

FIG. 6 depicts six representative controller responses, showing how ameasured process variable may approach a setpoint depending on how thecontroller is configured.

FIG. 7 depicts a representative controller response and depicts how ameasured process variable (PV) at a first setpoint (“initial steadystate value of PV”) may be driven to a second setpoint (“final steadystate value of PV”).

FIG. 8 is a fragmentary, isometric view of various components comprisingthe distal end of an ablation catheter that could be used with thepulsed RF control systems disclosed herein.

FIG. 9 is similar to FIG. 8, but depicts components of the distal end ofa non-irrigated catheter that could be used in combination with thepulsed RF control systems disclosed herein.

FIG. 10 is an exploded, isometric view of the catheter tip depicted inFIG. 8, showing additional components and features.

FIG. 11 is a side view of the conductive shell depicted in, for example,FIGS. 8 and 10.

FIG. 12 is an isometric view of the conductive shell depicted, forexample, in FIGS. 10 and 11.

FIG. 13 is a cross-sectional view showing the interior of the conductiveshell depicted in, for example, FIGS. 10-12.

FIG. 14 is an enlarged isometric view of the shank also depicted in, forexample, FIGS. 8-10.

FIG. 15 is an isometric, cross-sectional view of the various cathetertip components also depicted in FIG. 8.

FIG. 16 is similar to FIG. 15, but is a cross-sectional view taken at anangular orientation that bisects two of the lateral irrigation channels.

FIG. 17 is an enlarged, fragmentary, cross-sectional view showing apossible interconnection between the shell cylindrical body, the shank,and an RF lead wire.

FIG. 18 is a fragmentary, isometric, cross-sectional view of a priorart, solid platinum (or solid platinum iridium) irrigated catheter tipwith a polymer irrigation tube mounted in its proximal end.

FIG. 19 is similar to FIGS. 15 and 16, and depicts another fragmentary,isometric, cross-sectional view, but this time taken from an angularorientation that clearly shows a distal-most thermal sensor.

FIG. 20 is an isometric view of components of the tip also depicted in,for example, FIGS. 8, 10, 15, 16, and 19.

FIG. 21 is similar to FIG. 20, but shows the catheter tip components ina different orientation, revealing the distal-most thermal sensor; andthis view also includes the shank, which is not present in FIG. 20.

FIG. 22 is an isometric view of the thermally-insulative ablation tipinsert also depicted in FIG. 21.

FIG. 23 depicts the tip insert of FIG. 22 in a slightly differentangular orientation, revealing an arc-shaped channel or ditch thatextends toward the distal end of the catheter tip to position thedistal-most thermal sensor at that location.

FIG. 24 depicts a thermally-insulative ablation tip insert for anon-irrigated embodiment of a catheter tip, such as the embodimentdepicted in FIG. 9.

FIG. 25 is most similar to FIG. 8, but depicts an alternative embodimentcomprising one or more isolated temperature-sensing islands.

FIG. 26 is most similar to FIG. 12, but depicts a multilayer embodimentof the conductive shell.

FIG. 27A schematically depicts magnetic flux lines reacting to adiamagnetic sub stance.

FIG. 27B schematically depicts magnetic flux lines reacting to aparamagnetic sub stance.

FIG. 27C schematically depicts magnetic flux lines reacting to aferromagnetic sub stance.

FIG. 28 is most similar to FIG. 20, but depicts an embodiment of the tipinsert on which both distal and proximal temperature sensors aremounted.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a highly-schematic representation of one embodiment of asystem 10 for delivering pulsed RF energy to an ablation catheter 12during catheter ablation, showing possible communication pathways 14,16, 18 between primary components in this embodiment. This figuredepicts a generator 20 operatively connected to a pulse control box 22,which is operatively connected to the ablation catheter 12. In thisfigure, a number of possible wired and/or wireless communicationpathways are shown. For example, a dashed line 14 represents temperaturefeedback from the catheter to the pulse control box 22 of readings fromat least one temperature sensor mounted in the tip of the catheter 12.In this embodiment, and in all of the embodiments described herein, thecatheter may comprise multiple thermal sensors (for example,thermocouples or thermistors), as described further below. If thecatheter comprises multiple temperature sensors mounted in its tipregion, the feedback shown in FIG. 1 from the catheter to the pulsecontrol box may be, for example, the highest reading from among all ofthe individual temperature sensor readings, or it may be, for example,an average of all of the individual readings from all of the temperaturesensors.

In FIG. 1, two communication options, represented by double-headed arrow24 and single-headed arrow 26, are shown for delivering information tothe generator 20 or exchanging information between the pulse control box22 and the generator 20. The communication pathway 18 between thegenerator 20 and the pulse control box 22 could comprise, for example,multiple, separate electrical connection (not separately shown) betweenthe generator 20 and the pulse control box 22. One of thesecommunication lines could be, for example, a separate (possiblydedicated) line for communicating to the generator the highesttemperature measured by any of a plurality of temperature sensorsmounted in the catheter tip. This could be used to trigger atemperature-based shutdown feature in the generator for patient safety.In other words, the temperature reading or readings from the cathetermay be sent to the pulse control box, which may then feed the highesttemperature reading to the generator so that the generator can engageits safety features and shut down if the temperature reading appears tobe getting undesirably or unsafely high.

In an alternative configuration, the generator 20 “thinks” it isdelivering RF energy to the catheter, but that energy is being deliveredinstead to the pulse control box 22. The pulse control box thendetermines, based upon the temperature feedback that it receives fromthe catheter, whether to drive the catheter at the power level comingfrom the generator or, alternatively, to pulse the delivery of RF energyto the catheter tip. In this configuration, the generator may be blindto the fact that the pulse control box 22 is determining whether to sendpower to the catheter tip or to momentarily suspend delivery of energyto the catheter tip as a means of effectively controlling tissuetemperature by monitoring and controlling catheter tip temperature.

FIG. 2 is similar to FIG. 1, but depicts the components arranged in aslightly different configuration in an alternative embodiment of asystem 10′ for delivering pulsed RF energy during catheter ablation. InFIG. 2, the pulse control box 22 is again receiving temperature feedbackfrom the catheter 12 along communication pathway 14. However, in FIG. 2,the pulse control box 22 is “telling” the generator (e.g., alongcommunication pathway 18′) to switch “off” and “on” based on the sensedtemperature from the catheter 12. The generator 20 then delivers pulsedRF energy to the catheter 12 via communication pathway 28. In thissystem 10′ for delivering pulsed RF energy, as in the system 10 depictedin FIG. 1 and discussed herein, the power can remain at a desired powerlevel (e.g., 50 or 60 Watts) rather than being reduced to an ineffectivelevel when excessive temperature is sensed by the catheter tip. Inparticular, rather than reducing the power to control temperature, thepower is delivered in a pulsed manner; and it is the control of theenergy pulses, including control of the length of the time gaps betweenpulses, that is used to control the tip temperature as a surrogate forcontrolling the tissue temperature. As a further alternative for how thesystem 10′ depicted in FIG. 2 may operate, the generator 20 may receivetemperature feedback via communication pathway 28 and then passtemperature feedback information to the pulse control box 22, whichwould then control the generator 20 as described above.

FIG. 3 is similar to FIGS. 1 and 2, but depicts a system 10″ with adedicated central processing unit (CPU) 30 interfacing with thecomponents 12, 20, 22 also depicted in FIGS. 1 and 2. As shown in thisfigure, a dedicated CPU is among the components in the system 10″ fordelivering pulsed RF energy during ablation. This figure also shows anumber of potential communication pathways between and among the variouscomponents, including, for example, a temperature feedback pathway 32between the catheter and the CPU, the temperature feedback pathway 14between the catheter and the pulse control box 22, a communicationpathway 34 between the generator 20 and the CPU 30, a communicationpathway 18″ between the generator and the pulse control box, thecommunication pathway 28 between the generator 20 and the catheter 12,and a communication pathway 36 between the CPU and the pulse controlbox. The following are various possible combinations of pathways thatcould be used, assuming the overall system comprises at least the fourcomponents 12, 20, 22, 30 shown in this figure:

-   -   A. 14, 18″, 28, 32, 34, 36 (all)    -   B. 14, 28, 34, 36    -   C. 14, 34, 36    -   D. 14, 18″, 36    -   E. 32, 34, 36    -   F. 18″, 32, 36    -   G. 18″, 32, 34    -   H. 14, 18″, 34

As represented by the first set (i.e., set “A” above) of examplepathways noted above, all six communication pathways 14, 18″, 28, 32,34, 36 depicted in FIG. 3 could be used in a system for deliveringpulsed RF energy during a catheter ablation procedure. Alternatively,and as merely one more example, communication pathways 14, 28, 34, and36 may be the only four communication pathways required in the controlsystem. This is the second example listed above (i.e., set “B”). In eachof these communication pathway examples, it is assumed that thegenerator 20 is always connected to the catheter 12 in some way (asrepresented in FIG. 3 by the solid line 28 extending between thegenerator and the catheter). Thus, in yet another example operatingscenario, the generator 20 may directly receive temperature feedbackfrom the catheter 12 along, for example, communication pathway 28. Thegenerator 20 could then share that temperature feedback information withthe dedicated CPU 30 and/or the pulse control box 22 via one or more ofthe communication pathways 18″, 34, 36. Yet another possible alternativeto the system 10″ depicted in FIG. 3 would be to switch the locations ofthe pulse control box 22 and the generator 20, similar to theconfiguration depicted in FIG. 1, but also include the dedicated CPU 30depicted in FIG. 3. In this latter optional configuration, there may bea communication pathway (not shown) directly connecting the pulsecontrol box 22 to the catheter 12 (similar to communication pathway 16in FIG. 1).

FIG. 4 schematically depicts a catheter 12 in use in a patient 38 andconnected to a generator 40 comprising a pulsed RF control systemaccording to the present disclosure. This figure depicts a portion of ahuman torso of the patient 38, a heart, a representative catheter tiplocated in the heart, a representative catheter handle, and the RFgenerator. As shown in this figure, the catheter is assumed to beconnected to the RF generator 40. In this configuration, the pulsecontrol hardware, software, and/or firmware is built into the generatoritself.

FIG. 5 is a flowchart depicting one possible control flow, includingvarious optional steps, for delivering pulsed RF energy to an ablationcatheter. In this representative, and not limiting, example of controlflow, the process commences at block 502. At block 504, the generator isplaced in a “power-control” mode. Next, at block 506 the generator poweris set to a desired power level for a desired initial time. In thisrepresentative flowchart, that initial power level is shown as 50 Wattsand the initial time is shown as 60 seconds; however, both of these aremerely sample values. If, for example, a physician is ablating a portionof the heart that lies near the esophagus, then the physician may chooseto use a lower power setting (e.g., 15 Watts) since the physician maydesire to create a relatively shallow lesion (e.g., a 1 mm deep lesion).At block 508, the pulse control may be set to setpoint 1. If, forexample, the pulse control box 22 (see, for example, FIG. 1) is a PIDcontroller (also known as a proportional-integral-derivative controlleror a three-term controller), setpoint 1 may relate to the measuredprocess variable (PV). That measured process variable may be thetemperature feedback coming from the catheter tip during the ablationcycle. As may be understood by one of skill in the relevant art, a PIDcontroller calculates an error value as the difference between ameasured process variable—e.g., measured tip temperature—and a desiredsetpoint—e.g., a desired tip temperature. The controller then attemptsto minimize the error by adjusting the process through use of amanipulated variable (MV)—e.g., the time that a selected power isactively delivered to an ablation tip. The three parameters in a PIDcontroller are as follows:

-   -   1. the proportional value (P)—depends on present error;    -   2. the integral value (I)—accumulation of past errors; and    -   3. the derivative value (D)—predictive of future errors based on        current rate of change.

In an effort to achieve a gradual convergence to the setpoint, which, asdiscussed herein, may be desired catheter tip temperature, thecontroller calculates a weighted sum of P, I, and D, and then uses thatvalue to adjust the process—here by adjusting the time when RF power isdelivered to the ablation tip (e.g., by pulsing the delivery of RFenergy to the tip). In one embodiment of the system described herein, auser is allowed to “tune” the three values, namely the P, I, and Dvalues. The controller may be a separate controller as discussed hereinand shown in FIGS. 1-3 (e.g., pulse control box 22 in these figures), ormay be implemented as a microcontroller or a programmable logiccontroller (PLC) or in other firmware or software, all of which may be,for example, built directly into the generator 40 as shown in, forexample, FIG. 4. In the control systems described herein, RF power isturned “on” and “off” based on the temperature feedback as it isinterpreted and analyzed by the pulse control box. In block 510, theablation cycle begins.

In block 512, the control system monitors the catheter tip temperature.As noted above, this would be the “PV” value in a PID controller. Asrepresented by block 514 and its loop back to block 512, as long as thetip temperature is not close to setpoint 1, the system continues topermit the delivery of full RF power to the ablation tip and continuesto monitor catheter tip temperature at block 512. Once the measured tiptemperature is approximately at the value of setpoint 1 (e.g., 40° C. inone example), the pulse control box (e.g., the PID controller) wouldbegin to pulse the RF energy being delivered to the catheter tip (seeblock 516) in an effort to keep the tip temperature approximately atsetpoint 1.

Continuing to refer to the flowchart in FIG. 5, at block 518, thetemperature setting on the pulse control box 22 is changed to setpoint2, which may be, for example, a higher value than setpoint 1. As shownin FIG. 5, in this example setpoint 2 is 55° C. At this point in theprocess, and in order to increase the tip temperature from setpoint 1 tosetpoint 2, the full RF power may be delivered to the catheter tip (seeblock 520). In other words, at least initially, the system may stopdelivering pulsed RF energy to the ablation tip as the system tries todrive the tip temperature from the setpoint 1 temperature to thesetpoint 2 temperature. In block 522, the system monitors the tiptemperature. In decision block 524, the system compares the temperatureat the ablation tip to setpoint 2. If the tip temperature is not yetapproximately equal to the value of setpoint 2, the system repeatedlyreturns to block 522 and continues to monitor the tip temperature beingreported to the pulse control box. Once the tip temperature isapproximately equal to the value of setpoint 2, control transfers fromblock 524 to block 526 in FIG. 5.

Block 526 is similar to block 516 and, at this point, the control systembegins again to pulse the delivery of RF energy in an effort to keep thetip temperature approximately at setpoint 2 without overheating thetissue. In decision block 528, the system next attempts to determinewhether the ablation is complete (e.g., a physician may stop calling forthe delivery of ablation energy). Once it is determined that theablation is complete (e.g., when, a physician determines that sufficientRF energy has been delivered to the tissue), control transfers to block530; and all delivery of RF energy to the ablation tip is stopped.

As mentioned, in one of the sample embodiments described herein, the PIDcontroller receives values for setpoint 1 and setpoint 2, which may beentered by a user. The PID controller also receives the measuredtemperature (or multiple measured temperatures if multiple temperaturesensors are present) from the catheter tip. The controller thendetermines when to permit delivery of full power RF energy or pulsed RFenergy to the ablation tip, including, in the latter case, the length ofthe pulses (i.e., the time periods when RF energy is being delivered tothe catheter tip) and the length of the time periods when no RF energyis being delivered to the catheter tip. The length of the pulses and thelength of the non-pulse time periods may vary continuously. That is, theduration of two adjacent pulses may be different, and the length of twoadjacent non-pulse time periods may be different. The PID controllerdetermines algorithmically when to turn the RF power “on” and “off” asit receives real-time (or near-real-time) tip temperature feedback fromthe ablation catheter.

FIG. 6 depicts six representative controller response curves, showinghow a measured process variable (which may be the measured tiptemperature in the control systems disclosed herein) may approach asetpoint (which may be the desired tip temperature in the controlsystems disclosed herein), depending on how the controller isconfigured. In the ablation controllers discussed herein, the controllerresponse curve labeled “Long Integral Action Time” in FIG. 6 may be adesirable controller response as the tip temperature is driven from itsstarting temperature to the desired ablation temperature. In particular,in this curve, which is located in the middle of the left three curvesin FIG. 6, the temperature would never exceed the setpoint temperature(e.g., setpoint 1 or setpoint 2 in FIG. 5), but would reach the setpointtemperature in a timely and efficient manner.

FIG. 7 depicts a representative controller response curve and depictshow a measured process variable (PV) at a first setpoint (“initialsteady state value of PV”) may be driven to a second setpoint (“finalsteady state value of PV”). This ‘dual setpoint’ configuration isrepresented in the full flowchart of FIG. 5, which is described above.It should be noted, however, that such a dual setpoint control scheme isnot required. In other words, an effective controller could drive thecatheter tip temperature directly to the setpoint ultimately desired,without driving to a first value (e.g., setpoint 1) and then driving toa second value (e.g., setpoint 2). Hence, blocks 518-526 are labeled“optional” in FIG. 5. If these five blocks were not present, the “No”decision line from block 528 would go to block 516. The control systemwould then be configured to drive to a single setpoint. That said, thereare potential advantages to keeping all blocks of the control schemedepicted in FIG. 5. For instance, the control system of FIG. 5 may havesome distinct safety advantages. For example, setpoint 1 could be aninitial temperature that is somewhere between the starting temperatureof the ablation tip and the ultimate desired temperature for theablation tip. If the system is able to reach the setpoint 1 valueeffectively and while remaining under control, that would provide theuser with confidence that the tip is in contact with the tissue and thatthe controller is working properly before the tip temperature reaches apotentially dangerously-high temperature. Once setpoint 1 is reached(i.e., where control transitions from block 514 to block 516 in FIG. 5),the user with have confidence that the controller is functioningproperly and could then, at block 518 of FIG. 5, input a higher(ultimately desired) working temperature for creating lesions.

To enable the ablation temperature control system described above towork most effectively, it may be desirable to have an ablation tiphaving a relatively low thermal mass (also known as ablation tip havinghigh thermal sensitivity). If the ablation tip has a relatively lowthermal mass, it more rapidly heats (i.e., it comes to temperaturequickly) and cools (i.e., it does not remain hot for long after power isremoved), enabling tighter control of the tip temperature and less“coasting” of the tip temperature past a desired setpoint as well asmore rapid reduction in tip temperature when RF power is removed fromthe tip. In fact, such a tip may cool down at the same rate as thetissue, which would inform the user whether the tip became dislodgedduring ablation. Remaining FIGS. 8-25, which are described furtherbelow, depict various embodiments and components of ablation cathetertips that can be used effectively with the pulsed RF control systemsdescribed herein. The catheter tips disclosed herein are not necessarilythe only tips that could be used with the pulsed RF control systemsdescribed herein.

FIG. 8 is a fragmentary, isometric view of various components comprisingan embodiment of a tip 42 at the distal end of an ablation catheter thatcould be used with the pulsed RF control systems disclosed herein. Inthis embodiment, a conductive shell 44 (e.g., a platinum shell, aplatinum iridium shell, or a gold shell) with irrigation ports or holesis present at the most distal end of the catheter components shown inFIG. 8. The conductive shell 44 (which may weigh, for example, 0.027 g)includes a shell distal end portion 48 and a shell proximal end portion50, which may comprise one or more parts or components. In thisparticular embodiment, the shell 44 includes six irrigation holes 46,two of which are visible in this isometric view. Also visible in FIG. 8is an optional shank 52 comprising an annular or washer-shaped brim 54and a cylindrical open crown 56, which together define thetop-hat-shaped shank. In this embodiment, the conductive shell 44 andthe shank 52 effectively encase an ablation tip insert 58, the proximalsurface 60 of which is partially visible in FIG. 8. An electrical leadwire 62 is shown connected (e.g., by soldering or welding) to the shank52. Alternatively, the electrical lead wire 62 may be directly connectedto the conductive shell 44. A number of lead wire pairs 64 for thetemperature sensors comprising part of the tip may be seen extendingrearwardly or proximally in FIG. 8. Finally, FIG. 8 also shows twocomponents of an irrigation tube assembly 66 extending proximally inFIG. 8 (i.e., rightwardly in this figure). Although the conductive shell44 depicted in the figures includes six irrigation holes 46, more orfewer holes may be used, and the size of the holes may be larger, orsmaller, or a mix of larger and smaller holes.

Using the control systems described herein, it may be completelyunnecessary to irrigate the ablation tip. FIG. 9 is similar to FIG. 8,but the conductive shell 44′ depicted in FIG. 9 does not include anyirrigation ports or holes through it (compare element 46 in FIG. 8).Thus, this is a non-irrigated catheter tip 42′ that could be used incombination with the pulsed RF control systems described herein. Most ofthe discussion below focuses on the irrigated catheter tip embodiment 42of FIG. 8, but much of what is said below regarding the embodiment 42depicted in FIG. 8 applies equally well to the nonirrigated catheter tipembodiment 42′ depicted in FIG. 9, with the exception of the discussionof the irrigation features. It should also be noted that, although theirrigation tube assembly 66 (shown in FIG. 8) is not necessary in thenon-irrigated catheter tip embodiment 42′ depicted in FIG. 9 (and, thus,is not shown in FIG. 9), the irrigation tube assembly 66 could bepresent on the non-irrigated catheter tip embodiment. Further, as alsoshown in FIG. 9, the proximal surface 60′ of the ablation tip insert ofthe non-irrigated embodiment 42′ may be slightly different from theproximal surface 60 (FIG. 8) of the ablation tip insert 58 (see alsoFIG. 10) of the irrigated embodiment 42 (FIG. 8). In particular, theproximal surface 60′ may not include the main channel 84, which isdiscussed further below in connection with FIG. 10. The non-irrigatedembodiment of FIG. 9 could, however, just as easily use the sameablation tip insert 58 and the irrigation tube assembly 66 shown in theirrigated catheter tip embodiment 42 of FIG. 8, which would make itpossible, for example, to manufacture both irrigated and non-irrigatedembodiments on a single assembly line, and would likely result in thetwo embodiments exhibiting more similar structural integrity during use.

FIG. 10, which is an exploded, isometric view of the catheter tip 42depicted in FIG. 8, is described next, starting with the elements shownin the upper left-hand portion of that figure and working toward thelower right-hand portion of the figure. FIG. 10 again depicts theconductive shell 44, but this time exploded away from the othercomponents of the tip shown in FIGS. 8 and 10, thereby revealingadditional features and components. To the right of the conductive shellin FIG. 10 is an assembly of an ablation tip insert 58 and onetemperature sensor 68 (e.g., a thermocouple). As may be seen in FIG. 10,the tip insert 58 includes a plurality of lateral irrigation channels 70that are sized and arranged to align with complementary irrigation holes46 through the conductive shell 44. To facilitate assembly, the diameterof the lateral irrigation channels 70 in the tip insert 58 may besmaller than the complementary holes 46 through the conductive shell 44.Thus, it would be less critical to precisely align the lateralirrigation channels with the holes through the conductive shell duringmanufacturing, and the exiting irrigant would have less of anopportunity to contact the conductive shell before reaching a bloodpool.

The tip insert, which may be a unitary piece, includes a main body 72and a stem 74. The tip insert 58 can be constructed from, for example,plastic (such as PEEK, which is polyether ether ketone) orthermally-insulative ceramic. In the depicted embodiment, the main bodyportion 72 includes a plurality of optional, longitudinally-extendingsensor channels or ditches 76. In FIG. 10, a thermal sensor 68 is shownmounted in one of these ditches 76. Each of the sensor ditches isseparated from the next adjacent sensor ditch by alongitudinally-extending shell seat 78. The plurality of shell seatsbetween the sensor ditches are configured to ride against, or very nearto, the inner surface of the conductive shell 44. Similarly, the stem 74of the tip insert 58 defines a plurality of longitudinally-extendingwire channels or ditches 80 separated by a plurality oflongitudinally-extending shank seats 82. The ditches 76, 80 areconfigured to carry temperature sensor lead wires on their path to theproximal end of the catheter. The shank seats 82 are sized andconfigured to ride against, or very near to, the inner surface of thecylindrical open crown portion 56 of the shank 52. The tip insert 58includes a main channel 84 having a circular cross-section that, asshown in the figures and as described further below, may include morethan one inner diameter.

Downward to the right of the tip insert 58 in FIG. 10 is an irrigationtube assembly 66. The irrigation tube assembly comprises, in thisembodiment, a central irrigation tube 86 and an optional seating sleeve88. The central irrigation tube 86 has a distal end 90 and a proximalend 92 and may be constructed from a polymer, such as polyimide. Thiscentral irrigation tube may extend proximally toward a catheter handle,or may extend proximally all the way to the catheter handle. Theoptional seating sleeve 88, as shown in the embodiment depicted in FIG.10, may include a cylindrical portion and a frustoconical boss. Theseating sleeve may be positioned at a desired longitudinal locationalong the outer surface of the central irrigation tube 86 and then maybe fixed in place (for example, by an adhesive or sonic welding or viasome other technique). The irrigation tube assembly would then bemounted in the tip insert by, for example, adhesive. If the optionalseating sleeve is not included (e.g., to simplify tip construction andmanufacturing), the central irrigation tube 86 could be adhered directlyto the tip insert 58. To the right of the irrigation tube assembly inFIG. 10 is the optional shank 52. Details of the shank are describedfurther below in connection with, for example, FIG. 14. To the right ofthe shank are five additional temperature sensors 68. In particular, inthis particular embodiment of the tip, six temperature sensors areradially disposed symmetrically about the catheter longitudinal axis 94(see, for example, FIG. 8). Since one of those six thermal sensors isdepicted already in position on the tip insert 58 in FIG. 10, theremaining five temperature sensors are shown in the lower right-handportion of FIG. 10, oriented and arranged so as to slip into theremaining five complementary sensor ditches 76 formed in the tip insert.

FIGS. 11-13 are additional views of the conductive shell 44 depicted in,for example, FIGS. 8 and 10. As shown in these figures, the conductiveshell may comprise a hemispherical or nearly-hemispherical domed distalend 48 and a cylindrical body 50. In the figures, a ‘seam’ 96 is shownbetween the domed distal end 48 and the cylindrical body 50. This may bemerely a circumferential transition line between the cylindrical bodyand the domed distal end of a unitary component; or, alternatively, itmay be the location where the cylindrical body is connected to the domeddistal end by, for example, welding. In one embodiment, the wallthickness 98 of the shell is 0.002 inches, but alternative wallthicknesses also work. The conductive shell could be formed ormanufactured by, for example, forging, machining, drawing, spinning, orcoining. Also, the conductive shell could be constructed from moldedceramic that has, for example, sputtered platinum on its externalsurface. In another alternative embodiment, the conductive shell couldbe constructed from conductive ceramic material.

FIG. 14 is an enlarged, isometric view of the shank 52 also depicted in,for example, FIGS. 8-10. The brim 54 may include a circumferentialoutward edge 100 that, as described below, may be connected by weldingor soldering to a surface (e.g., the inner surface) of the cylindricalbody 50 of the conductive shell. The shank includes a cylindrical opencrown 56 that also defines an inner surface. As described above, theinner surface of the cylindrical open crown is sized and configured toslide over the shank seats 82 defined on the stem of the tip insert 58.The cylindrical open crown of the shank also defines a proximal end oredge 102.

FIG. 15 is an isometric, cross-sectional view of various components ofthe catheter tip 42 also depicted in FIG. 8 and clearly shows twotemperature sensors 68 mounted in their respective temperature sensorditches 76. As may be clearly seen in this figure, the sensor ditchesmay include a wire ramp 104 that allows the thermal sensor lead wires 64to transition from the sensor ditches 76 (formed in the main body of thetip insert) to the wire ditches 80 (formed in the stem of the tipinsert). In this configuration, the circumferential outer edge 100 ofthe brim 54 of the shank 52 is shown riding against the inner surface ofthe cylindrical body of the conductive shell 50. The shank may be weldedor soldered to the conductive shell at this interface to ensure goodelectrical contact between the shank and the shell. In particular, sincethe tip electrode lead wire 62 may be electrically connected to thecylindrical open crown 56 of the shank 52 in this embodiment, the shankmust be conductively connected to the conductive shell 44 in a mannerthat permits transfer of energy from the tip electrode lead wire 62 tothe shank 52 and then to the conductive shell 44.

Looking more closely at the irrigation tube assembly 66 shown in FIG.15, it is possible to see that the distal end 90 of the centralirrigation tube 86 rides against an inner annular ledge 106 formed aspart of the tip insert 58. Further, the frustoconical boss defines adistally-facing ledge or lip that rides against the distal end of thestem 74 of the tip insert 58. Thus, the irrigation tube assembly seatsagainst both the proximal surface 60 of the tip insert 58 as well as theinner annular ledge 106 defined along the longitudinal irrigationchannel 84 extending through most of the tip insert 58. It should benoted that when the temperature sensors are in place in the tip insert,when the irrigation tube assembly is mounted in the tip insert, and whenthe conductive shell and the shank are in position, any voids in theassembled tip (other than the lateral irrigation channels 70) may befilled with potting material, providing a durable assembled set ofcomponents. It should also be noted that the outer surface of thetemperature sensors are mounted so as to at least be in close proximityto, and preferably so as to be in physical contact with, the innersurface of the conductive shell 44. As used herein, “in close proximityto” means, for example, within 0.0002 to 0.0010 inches, particularly ifa conductive adhesive or other bonding technique is used to bond thetemperature sensors to the inner surface of the shell. Depending on thespecific properties of the sensors, the construction and materials usedfor the shell, and the type of conductive adhesive or the other bondingtechnique employed, it is possible that enough temperature sensitivitymay be achieved despite even larger gaps between the sensors and theconductive shell, as long as the sensors are able to readily sense thetemperature of the tissue that will be touching the outer surface of theconductive shell during use of the catheter tip. Also, the distal endportions of the sensor ditches 76 may be shallower than the proximal endportions of the sensor ditches. In this manner, when a temperaturesensor 68 is mounted in its respective sensor ditch, the distal mostportion of the temperature sensor is “lifted” toward and possiblyagainst the inner surface of the cylindrical body of the conductiveshell 44. This helps to establish good thermal conductivity between theconductive shell and the thermal sensor or sensors mounted inside of theshell.

FIG. 16 is similar to FIG. 15, but is a cross-sectional view taken at aslightly different angular orientation from that shown in FIG. 15, tothereby reveal two of the lateral irrigation channels 70 configured todeliver irrigant 108 outside of the tip 42. Since the conductive shellis very thin in these embodiments, and since the tip insert isconstructed from an insulative material, the irrigant, when used, hasvery little ability or opportunity to influence the temperature of theconductive shell 44. As shown to good advantage in FIG. 16, the irrigantexiting the lateral irrigation channels touches the inner edges of theholes 46 through the conductive shell before exiting to the surroundingblood. This may be contrasted to what is shown in FIG. 18, which depictsa prior art catheter tip 42″. In particular, FIG. 18 depicts a solidplatinum (or platinum iridium) tip 110 with a polymer irrigation tube 86mounted in it. In this solid platinum tip (which may weigh, for example,0.333 g), the irrigant 108 flows through and directly contacts a portionof the platinum tip before reaching the lateral irrigation channels 70′and then exiting the tip. Thus, there is a relatively extended period oftime where the cool irrigant rides directly against the platinumcomprising the conductive tip. Thus, in the embodiment depicted in FIG.18, the irrigant has a much greater opportunity to influence thetemperature of the tip than does the irrigant in the embodiment depictedin, for example, FIG. 16.

Also, during ablation with a solid platinum tip 110, essentially theentire tip must heat up before a sensor embedded in the tip senses atemperature rise. Thus, not only does the portion of the tip in contactwith the tissue being treated heat up, but also the entire tip gets hot,even portions of the tip that are remote from the tissue being treated.Blood flow around the entire solid platinum tip robs heat from the tip,which further distorts the temperature sensed by a sensor embedded inthe solid platinum tip; and temperature averaging issues may come intoplay. For at least these reasons, the temperature sensor embedded in asolid platinum tip is less capable of accurately reporting thetemperature in the immediate vicinity of the tissue being treated. Incontrast, in embodiments such as the one depicted in FIGS. 15 and 16,with a relatively thin conductive shell 44 surrounding an insulative tipinsert 58, the temperature of the conductive shell in the immediatevicinity of the tissue-tip interface heats up quickly, and the sensor 68closest to that portion of the conductive shell rapidly senses andreports a temperature rise in the immediate vicinity of the tissue-tipinterface. It is not necessary for the entire tip to heat up before thesensor can report a temperature rise in the tissue, the blood flowingaround the entire tip thus has less of an opportunity to distort thesensed tip temperature, and fewer temperature averaging issues come intoplay.

FIG. 17 is an enlarged, fragmentary, cross-sectional view showing onepossible interconnection between the cylindrical body 50 of theconductive shell 44, the shank 52, and the RF lead wire 62. As shown inthis figure, a proximal edge 112 of the cylindrical body 50 of theconductive shell is bent around the circumferential outward edge 100 ofthe shank brim 54. The shank brim and the shell body are then connectedby welding or soldering, for example. Thus, energy coming from the RFlead wire 62 can be delivered to the shank crown 56, conducted to theshank brim 54, and then delivered to the cylindrical body 50 of theconductive shell.

FIG. 19 is similar to FIGS. 15 and 16, and depicts another fragmentary,isometric, cross-sectional view, but this time taken from an angularorientation that clearly shows a distal-most thermal sensor 114. Inparticular, this figure clearly depicts an arc-shaped channel 116extension extending from one of the sensor ditches 76. As shown in thisembodiment, the distal-most thermal sensor (i.e., a seventh thermalsensor in this embodiment) can thus be placed very near to the mostdistal portion of the tip 42. This distal-most thermal sensor is shownhaving a spherical shape in FIG. 19 and being placed ahead of (i.e.,distally of) one of the radially-disposed thermal sensors 68.

FIG. 20 is an isometric view of components of the tip also depicted in,for example, FIGS. 8, 10, 15, 16, and 19. In this figure, all six of theradially-disposed thermal sensors 68 are in place in their respectivesensor ditches 76. The seventh, distal-most thermal sensor may also bein place, but is not shown in this particular figure. This figure alsoclearly shows the frustoconical boss comprising part of the optionalseating sleeve 88 with its distally-facing surface or tip restingagainst the proximally-facing surface 60 of the tip insert 58.

FIG. 21 is similar to FIG. 20, but shows components of the catheter tipfrom a different view, wherein the distal-most thermal sensor 114 (i.e.,the seventh thermal sensor in this embodiment) is visible, and this viewalso includes the shank 52, which is not present in FIG. 20. In FIG. 21,the shank is in place over the stem of the tip insert, which helpsclarify the benefit of the wire ramps 104 connecting the sensor ditches76 to the wire ditches, both of which are formed in the tip insert.

FIG. 22 is an isometric view of just the thermally-insulative ablationtip insert 58 also depicted in FIG. 21, but without any other tipcomponents. All of the ablation tip inserts described herein arepreferably constructed from thermally-insulative material. They could beconstructed from, for example, ULTEM. In this particular embodiment, thetip insert includes six laterally-extending irrigation channels 70, eachof which has a longitudinal axis arranged substantially perpendicular tothe longitudinal axis of the tube channel that is itself arrangedsubstantially parallel to the catheter longitudinal axis 94. Thelaterally-extending irrigation channels connect a distal end of the tubechannel 84 to an outer surface of the tip insert. It should be notedthat the laterally-extending irrigation channels could be arranged at adifferent angle (i.e., different from 90°) relative to the tube channellongitudinal axis. Also, more or fewer than six laterally-extendingirrigation channels may be present in the tip insert. Again, the outersurface of the tip insert may define a plurality of sensor ditches 76,and these ditches may be separated by a plurality of shell seats 78.These sensor ditches may be, for example, 0.010 inches deep. The shellseats, as described above, may be configured to ride against, or verynear to, the inner surface of the conductive shell. A few of the sensorwire ramps are also clearly visible in FIG. 22. As previously described,the stem 74 of the tip insert may define a plurality of wire ditches 80separated by a plurality of shank seats 82 as shown in FIG. 22.

FIG. 23 depicts the tip insert 58 of FIG. 22 in a slightly differentorientation, revealing the arc-shaped channel 116 (or sensor ditchextension) that extends toward the distal-most end of the catheter tipto position the distal-most thermal sensor 114 (see, for example, FIG.21) at that location. It should be kept in mind that this arc-shapedchannel extension need not be present. It has been determined, however,that a number of advantages may be realized by positioning a thermalsensor as far distally on the catheter tip as possible. For example, inview of the rapid heat dissipation experienced by these catheter tips,it can be extremely helpful to sense temperature at this distal locationsince it may be in the best location for most accurately determining thetemperature of the surrounding tissue during certain procedures.

FIG. 24 depicts an alternative thermally-insulative ablation tip insert58′. This tip insert could be used in a non-irrigated embodiment of thecatheter tip 42′, such as the embodiment depicted in FIG. 9. Inparticular, as discussed above, the control systems for deliveringpulsed RF to ablation catheters described herein may completelyeliminate the need for the use of irrigation. With that in mind, FIG. 24depicts one possible configuration for a tip insert for use in anon-irrigated ablation catheter. This embodiment of the tip insert stillincludes sensor ditches 76 and sensor wire ditches 80 as describedabove.

Further, it should be understood that, in other embodiments of thethermally-insulative ablation tip insert (both irrigated andnon-irrigated embodiments), there may be more or fewer sensor ditches76. In fact, although the sensor ditches may facilitate placement of thesensors 68 on the insert (e.g., during catheter assembly), the outersurface of the main body of the tip insert may be smooth (or at leastditchless). In such an embodiment, the sensors may be aligned on thesmooth outer surface of the tip insert (and, possibly, held in place by,for example, adhesive). Then, when the conductive shell is in placearound the tip insert and the sensors 68 are in place between the outersurface of the tip insert and the inner surface of the conductive shell,the gaps or voids between the inner surface of the conductive shell andthe outer surface of the tip insert may be filled with material (e.g.,potting material or adhesive). It is worth noting that the sensors maybe put in place before or after the conductive shell is placed over thetip insert. For instance, the sensors may be mounted on (e.g., adheredto) the smooth outer surface of the tip insert forming atip-insert-sensor subassembly. Then, the conductive shell may be placedover that tip-insert-sensor subassembly before the remaining voidsbetween the tip-insert-sensor subassembly and the conductive shell arefilled. Alternatively, the conductive shell may be held in place overthe tip insert while one or more sensors are slid into the gap betweenthe outer surface of the tip insert and the inner surface of theconductive shell. Subsequently, the voids could again be filled. Thesealternative manufacturing techniques apply to all of the disclosedembodiments that comprise sensors mounted between a tip insert and aconductive shell member.

FIG. 25 is most similar to FIG. 8, but depicts one form of analternative embodiment of a catheter tip 42′″ comprising one or moreisolated temperature-sensing islands 118 which, in this embodiment,reside partially on the doomed distal end 48′ of the conductive shell44″ and partially on the cylindrical body 50′ of the conductive shell44″. Each of these temperature-sensing islands 118 is outlined orcircumscribed by a strip of insulative material 120 placed to reduce oreliminate any potential influence from irrigant flowing through thenearby holes 46′ in the conductive shell. In particular, if the cooledirrigant flowing through a hole through the conductive shellmeaningfully reduces the temperature of the conductive shell around thehole, that lower temperature would not be transmitted to a temperaturesensor mounted within the conductive shell below the temperature-sensingisland 118.

Although a single-layer conductive shell 44 (see, e.g., FIGS. 10-13 and15) constructed from a thin layer of gold, for example, may perform inan magnetic resonance (MR) environment without causing undesirable orunmanageable MR artifacts, a conductive shell comprising an outer layerof a paramagnetic material such as platinum or platinum iridium, forexample, may benefit from a multilayer construction as discussed below.

FIG. 26 is most similar to FIG. 12, but depicts a multilayer conductiveshell 44′″. A multilayer conductive shell may have just a multilayercylindrical body portion, just a multilayer domed distal end portion, orboth a multilayer domed distal end portion and a multilayer cylindricalbody. In the embodiment depicted in FIG. 26, both the domed distal endportion 48′″ and the cylindrical body 50′″ have a multilayerconstruction. As shown in this figure, the domed distal end portion 48′″comprises an inner layer 122 and an outer layer 124, and the cylindricalbody 50′″ similarly comprises an inner layer 126 and an outer layer 128.Again, however, it is not a requirement that the domed distal endportion and the cylindrical body must both be constructed with the samenumber of layers or with the same thickness of layers. Also, the wallsof the conductive shell 44′″ may, for example, be of a total thicknessthat is the same as, or nearly the same as, the thickness 98 (see FIG.12) of the single-layer conductive shell 44 described above. Theconductive shell could be formed or manufactured per, for example, thetechniques already described herein.

FIGS. 27A, 27B, and 27C schematically depict various materials orsubstances in a magnetic field (e.g., in an MR environment). Inparticular, FIG. 27A schematically depicts magnetic flux lines reactingto a diamagnetic substance (the lines of force tend to avoid thesubstance when placed in a magnetic field), FIG. 27B schematicallydepicts magnetic flux lines reacting to a paramagnetic substance (thelines of force prefer to pass through the substance rather than air),and FIG. 27C schematically depicts magnetic flux lines reacting to aferromagnetic substance (the lines of force tend to crowd into thesubstance). Platinum iridium (a paramagnetic material) is commonly usedfor constructing catheter tips. Thus, as may be discerned from lookingat FIG. 27B, a thin conductive shell (e.g., conductive shell 44 depictedin FIG. 12) constructed entirely from platinum or platinum iridium (orsome other paramagnetic material) may induce MR artifacts.

As mentioned above, a more MR compatible catheter tip may comprise, forexample, a single layer conductive shell 44 constructed entirely from adiamagnetic material (e.g., a thin gold conductive shell) or amultilayer conductive shell 44′″. In one example of an MR compatiblemultilayer conductive shell, the conductive shell 44′″ comprises a shelldistal end portion (shown as domed distal end 48′″ in FIG. 26) and ashell proximal end portion (shown as cylindrical body 50′″ in FIG. 26).In this embodiment, the conductive shell 44′″ may comprise a platinumiridium outer layer (or skin) 124, 128 and an inner layer (or liner orcore) 122, 126 constructed from a diamagnetic material (e.g., gold orcopper). In such an embodiment, the paramagnetic outer layer 124, 128and the diamagnetic inner layer 122, 126 ‘cooperate’ in a manner thatminimizes or mitigates against the generation of undesirable MRartifacts. In some multilayer embodiments (e.g., with a paramagneticouter layer and a diamagnetic inner layer), it can be beneficial to massbalance or volume balance the material comprising the layers of themultilayer conductive shell 44′″. Alternatively, the multilayerconductive shell 44′″ of the MR compatible catheter tip may have anouter layer constructed from a diamagnetic material (such as bismuth orgold) and an inner layer constructed from a paramagnetic material (suchas platinum or platinum iridium).

In yet another embodiment (not shown), a multilayer conductive shell maycomprise more than two layers. For example, the conductive shell maycomprise three layers, including a very thin outer layer of aparamagnetic material, a somewhat thicker or much thicker intermediatelayer of a diamagnetic material, and an oversized internal layer of anon-precious metal (or plastic or other material) sized to ensure thatthe finished geometry of the overall ablation tip is of a desired sizefor effective tissue ablation.

Materials that could be used for the inner layer or liner include, butare not limited to, the following: silicon (metalloid); germanium(metalloid); bismuth (post transition metal); silver; and gold. Silverand gold are examples of elemental diamagnetic materials that haveone-tenth the magnetic permeability of paramagnetic materials likeplatinum. Thus, one example multilayer shell configuration couldcomprise a platinum outer layer (or skin) and an inner layer (or lineror core) of gold or silver with a thickness ratio (e.g.,platinum-to-gold thickness ratio) of at least 1/10 (i.e., the platinumlayer being one-tenth as thick as the gold layer). In another example, amultilayer conductive shell configuration 44′″ could comprise a platinumouter layer and a bismuth inner layer with a thickness ratio (e.g.,platinum-to-bismuth thickness ratio) of at least ½ (i.e., the platinumouter layer being one-half as think as the bismuth inner layer) sincebismuth has a permeability that is about one-half the permeability ofplatinum. The layers may also be constructed from alloys, which may beused, for example, when a pure element material might otherwise bedisqualified from use in the construction of a catheter tip.

FIG. 28 is most similar to FIG. 20, but depicts an embodiment havingboth distal temperature or thermal sensors 68 and proximal temperatureor thermal sensors 68′ mounted on a tip insert. As depicted in FIG. 28,a plurality of temperature sensors 68′ may be deployed around or nearthe proximal end of the tip 42. These temperature sensors 68′ could bemounted, for example, on the ablation tip insert as already describedabove. Although FIG. 28 depicts an ablation tip insert 58 for anirrigated tip 42, the proximal temperature sensors 68′ may also be usedin nonirrigated embodiments such as the tip 42′ depicted in FIG. 9. Theproximal thermal sensors 68′ may be deployed, for example, in anangularly-spaced configuration similar to the configuration of the sixradially-disposed distal temperature sensors 68 shown in, for example,FIGS. 15, 19, 20, and 21 (but located near the proximal end of the mainbody 72 of the ablation tip insert 58 rather than its distal end). Thetemperature sensor configuration depicted in FIG. 28 would provide ahigher-resolution ‘picture’ of the thermal profile of the tip and,therefore, a better understanding of tissue temperature near thecatheter tip during ablation. This is particularly beneficial when sucha tip construction is used with the pulsed RF control systems disclosedherein.

Catheter tips having a variety of thermometry configurations could bedeployed successfully with the pulsed RF control systems describedherein. Thus, although the representative catheter tips described hereininclude six or twelve radially-disposed temperature sensors and onedistal temperature sensor placed close to the distal end of the cathetertip, the invention is not limited to such seven-sensor andthirteen-sensor configurations.

Also, catheters comprising various segmented tip designs may work togood advantage with the control systems described above. Some such tipconfigurations are disclosed in U.S. patent application No. 61/896,304,filed 28 Oct. 2013, and in related international patent application no.PCT/US2014/062562, filed 28 Oct. 2014 and published 7 May 2015 inEnglish as international publication no. WO 2015/065966 A2, both ofwhich are hereby incorporated by reference as though fully set forthherein.

It should also be noted that the control systems described herein mayuse a “rolling thermocouple,” which would, for example, measure thetemperature output from each of a plurality of thermocouples every 20msec (for example) and report the highest of these temperatures to thepulse control box and, potentially, directly to the generator (at leastfor safety shutdown reasons). In this manner, and in view of the lowthermal mass of the ablation tips described herein, the controller isalways working with the most accurate representation of the actualtissue temperature. In particular, since the device has low thermalmass, any temperature sensors facing away from the tissue during use ofthe catheter in an ablation procedure would cool rapidly and theirreadings could be ignored or discounted, whereas the temperature sensoror sensors closest to the portion of the catheter tip that is in contactwith tissue would heat rapidly and would, therefore, provide atemperature reading that is closest to the actual temperature of thetissue being ablated. Thus, by using only the temperature reading fromthe hottest temperature sensor (or the two or three hottest temperaturesensors) at any given time, the system is able to rapidly adjust for thewidely varying readings being received from the thermal sensors as thecatheter tip is rotated or pushed into tissue during actual use.

Although several embodiments have been described above with a certaindegree of particularity, those skilled in the art could make numerousalterations to the disclosed embodiments without departing from thepresent disclosure. It is intended that all matter contained in theabove description or shown in the accompanying drawings shall beinterpreted as illustrative only and not limiting. Changes in detail orstructure may be made without departing from the present teachings. Theforegoing description and following claims are intended to cover allsuch modifications and variations.

Various embodiments are described herein of various apparatuses,systems, and methods. Numerous specific details are set forth to providea thorough understanding of the overall structure, function,manufacture, and use of the embodiments as described in thespecification and illustrated in the accompanying drawings. It will beunderstood by those skilled in the art, however, that the embodimentsmay be practiced without such specific details. In other instances,well-known operations, components, and elements have not been describedin detail so as not to obscure the embodiments described in thespecification. Those of ordinary skill in the art will understand thatthe embodiments described and illustrated herein are non-limitingexamples, and thus it can be appreciated that the specific structuraland functional details disclosed herein may be representative and do notnecessarily limit the scope of the embodiments, the scope of which isdefined solely by the appended claims.

Reference throughout the specification to “various embodiments,” “someembodiments,” “one embodiment,” “an embodiment,” or the like, means thata particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment.Thus, appearances of the phrases “in various embodiments,” “in someembodiments,” “in one embodiment,” “in an embodiment,” or the like, inplaces throughout the specification are not necessarily all referring tothe same embodiment. Furthermore, the particular features, structures,or characteristics may be combined in any suitable manner in one or moreembodiments. Thus, the particular features, structures, orcharacteristics illustrated or described in connection with oneembodiment may be combined, in whole or in part, with the featuresstructures, or characteristics of one or more other embodiments withoutlimitation.

It will be appreciated that the terms “proximal” and “distal” may beused throughout the specification with reference to a clinicianmanipulating one end of an instrument used to treat a patient. The term“proximal” refers to the portion of the instrument closest to theclinician and the term “distal” refers to the portion located furthestfrom the clinician. It will be further appreciated that for concisenessand clarity, spatial terms such as “vertical,” “horizontal,” “up,” and“down” may be used herein with respect to the illustrated embodiments.However, surgical instruments may be used in many orientations andpositions, and these terms are not intended to be limiting and absolute.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialsdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as explicitly set forth hereinsupersedes any conflicting material incorporated herein by reference.Any material, or portion thereof, that is said to be incorporated byreference herein, but which conflicts with existing definitions,statements, or other disclosure material set forth herein will only beincorporated to the extent that no conflict arises between thatincorporated material and the existing disclosure material.

What is claimed is:
 1. A method of controlling a temperature of ahigh-thermal-sensitivity tip of an ablation catheter while creating alesion in cardiac tissue, comprising: placing a generator in apower-control mode; configuring the generator to continually deliverradio frequency (RF) power to the high-thermal-sensitivity tip (i) at apower level in a range of 50-60 Watts and sufficient to create thelesion; and (ii) for an initial time; setting a pulse control box, whichis operatively connected to the generator but physically separate fromthe generator, to a first setpoint that is a temperature in the range of40-55° C.; monitoring the temperature of the tip; commencing pulsedcontrol of the RF power delivered to the tip when the monitored tiptemperature approaches the first setpoint to keep the monitored tiptemperature approximately at the first setpoint without overheating thetissue, while also maintaining the power level in the range of 50-60Watts; reestablishing continual RF power delivery to the tip after themonitored tip temperature reaches the first setpoint; changing the pulsecontrol box to a second setpoint that is a temperature higher than thefirst setpoint and no more than 55° C.; comparing the monitored tiptemperature to the second setpoint; and re-commencing pulsed control ofthe RF power delivered to the tip after the monitored tip temperatureapproaches the second setpoint to keep the monitored tip temperatureapproximately at the second setpoint without overheating the tissue,while also maintaining the power level in the range of 50-60 Watts;wherein the pulse control box comprises aproportional-integral-derivative (PID) controller, wherein the PIDreceives the monitored tip temperature as a measured process variable,and wherein the PID controller is configured to continually compare themonitored tip temperature to the first setpoint or the second setpoint,and to commence the pulsed control of the RF power to the ablationcatheter when the monitored tip temperature approaches the firstsetpoint or the second setpoint.
 2. The method of claim 1, wherein atleast the setting, monitoring, and commencing steps are carried out bythe PID controller, a microcontroller, a programmable logic controller,firmware, and/or software.
 3. The method of claim 1, wherein the firstsetpoint comprises an initial steady state value of the tip temperature.4. The method of claim 1, wherein the configuring step further comprisessetting the initial time to 60 seconds.
 5. The method of claim 1,wherein the first setpoint is a desired initial tip temperature.
 6. Themethod of claim 5, wherein the pulse control box is configured toachieve a gradual convergence of the tip temperature to the firstsetpoint.
 7. The method of claim 1 further comprising continuing todeliver the pulsed RF power to the tip until the lesion is complete. 8.The method of claim 1, wherein the pulsed control of the RF power in there-commencing step is controlled to maintain the tip temperature at thesecond setpoint.
 9. The method of claim 8, wherein the pulsed control ofthe RF power in the re-commencing step further comprises varying a firsttime period when RF power is actively delivered to the tip as well asvarying a second time period when RF power is prevented from beingdelivered to the tip.
 10. The method of claim 1, wherein the firstsetpoint comprises an initial steady state value of the tip temperature,and wherein the second setpoint comprises a final steady state value ofthe tip temperature.
 11. A method for controlling the delivery of energyto an ablation catheter during an ablation procedure, the methodcomprising: setting an ablation generator to a power-control mode;inputting a RF ablation power level in a range of 50-60 Watts andsufficient to create a lesion in cardiac tissue; inputting a temperaturesetpoint into a pulse control box; initiating an ablation cycle;monitoring a temperature of an ablation tip of the catheter, wherein theablation tip has a low thermal mass; and commencing pulsed control of RFablation power delivered to the ablation tip when the monitored ablationtip temperature reaches or closely approaches the temperature setpointto keep the monitored ablation tip temperature approximately at thetemperature setpoint without overheating the tissue, while maintainingthe RF ablation power level in the range of 50-60 Watts; wherein theablation generator is operatively connected to, but physically separatefrom, the pulse control box; wherein the pulse control box comprises aPID controller, wherein the PID controller receives the monitoredablation tip temperature as a measured process variable, and wherein thePID controller is configured to continually compare the monitoredablation tip temperature to the temperature setpoint and to commence thepulsed control of RF ablation power delivered to the ablation tip whenthe monitored ablation tip temperature approaches the temperaturesetpoint.
 12. The method of claim 1, wherein the second setpointcomprises an subsequent steady state value of the tip temperature.